Field of the Invention
The present invention relates to Assisted Global Positioning Systems (A-GPS). More particularly, the present invention relates to providing assistance data to a mobile communication device.
Background of the Invention
Mobile communication devices are becoming increasingly ubiquitous. Cellular transceivers can be found in several portable and fixed devices that can further communicate over other types of networks. For instance, a cellular telephone can include a Global Positioning System (GPS) receiver as part of an Assisted GPS (A-GPS) system. To provide location information for a mobile communication device, a logic on the device queries the cellular network to obtain assistance data. The assistance data enables the GPS receiver to tune in to signals from a specific satellite or set of satellites. If the device is successfully able to calculate a geographical position from the received GPS signals, that location information can be applied to several location-based services, for instance, live weather, directions, security, and so on.
The query typically includes, inter alia, an identifier of a cell (Cell ID) that the device is communicating with. Assistance data in turn includes a list of satellites specific to the location of the cell, ephemeris information for each satellite, etc. Ephemeris information lists positions for specific satellites at a given time, and therefore turns obsolete in a few hours. Consequently, devices frequently query the network for assistance data. This consumes valuable resources such as bandwidth, channels, etc. Furthermore, the lack of a GPS signal can severely limit the functionality of these devices. If an A-GPS device is unable to calculate a location for a number of reasons, such as poor satellite reception, etc., an error message is returned, and the entire query fails. This means that all the data is needlessly transmitted in the user plane when it is not being used at the device.
What is needed is a technique for providing a location of a mobile communication device that is efficient and reliable.